Spot printing of color-forming microcapsules and co-reactant therefor

ABSTRACT

Copy sheets are provided having a localized coating of microcapsules by passing an uncoated paper web through a roll nip formed from a first roll and a raised portion of a second roll, wherein the first roll is an impression roll and the second roll is a printing roll having only a portion of its surface provided with a resilient material to provide a raised, resilient printing head on the second roll. A suspension of microcapsules containing a chromogenic material is coated onto the paper web as it passes between the first and second rolls in a configuration corresponding to the resilient printing head. The coated paper web is then passed to a drying zone where the microcapsular coating is dried. The same technique is used to provide a local coating of an electron-accepting material, such as acidic clay, on a receiving sheet, which may be used in combination with a local microcapsule coating which may be superimposed over the clay coating. Upon rupture of the microcapsules, the chromogenic material is released therefrom and reacts with the acidic clay to provide a localized image. In this manner a minimum of microcapsules and clay are required to produce a transfer copy system.

United States Patent [1 1 Vassiliades Oct. 21, 1975 SPOT PRINTING OFCOLOR-FORMING MICROCAPSULES AND CO-REACTANT THEREFOR Anthony E.Vassiliades, Deerfield, 111.

[73] Assignee: Champion International Corporation, New York, NY.

22 Filed: Oct. 18, 1973 211 App1,No.:407,654

[75] Inventor:

[56] 1 References Cited UNITED STATES PATENTS 3,016,308 1/1962 Macaulay117/36.l 3,086,879 4/1963 Lassiter 117/38 3,230,106 1/1966 West 117/383,418,250 12/1968 Vassiliades 252/316 3,466,184 9/1969 Bowler et a1117/36.2

3,732,141 5/1973 Brockett et al. 117/36.8 3,793,066 2/1974 Frenken et al117/1 1111 Primary ExaminerThomas J. Herbert, Jr. Attorney, Agent, orFirm-Roylance, Abrams, Berdo & Kaul 5 7 ABSTRACT Copy sheets areprovided having a localized coating of microcapsules by passing anuncoated paper web through a roll nip formed from a first roll and araised portion of a second roll, wherein the first roll is an impressionroll and the second roll is a printing roll having only a portion of itssurface provided with a resilient material to provide a raised,resilient printing head on the second roll. A suspension ofmicrocapsules containing a chromogenic material is coated onto the paperweb as it passes between the first and second rolls in a configurationcorresponding to the resilient printing head. The coated paper web isthen passed to a drying zone where the microcapsular coating is dried.The same technique is used to provide a local coating of anelectron-accepting material, such as acidic clay, on a receiving sheet,which may be used in combination with a local microcapsule coating whichmay be superimposed over the clay coating. Upon rupture of themicrocapsules, the chromogenic material is released therefrom and reactswith the acidic clay to provide a localized image. In this manner aminimum of microcapsules and clay are required to produce a transfercopy system.

16 Claims, 4 Drawing Figures US. Patent Oct. 21, 1975 ow mm SPOTPRINTING OF COLOR-FORMING MICROCAPSULES AND CO-REACTANT THEREFOR Thisinvention relates to the realized application of color-forming reactantsto a substrate. More particularly, this invention relates to spotprinting of an aqueous microcapsular dispersion, wherein themicrocapsules contain a chromogenic material, and an electronacceptingco-reactant for said chromogenic materials onto a paper substrate bymeans of an offset printing procedure.

Carbonless copy paper and particularly the transfer copy systems havefound a widespread commercial acceptance. A popular form of transfercopy system involves the use of microcapsules which contain a colorlessdye intermediate material, such as crystal violet lactone, which isdispersed or dissolvedin an oil. The microcapsules are coated onto atransfer sheet, and upon rupture of the microcapsules under thelocalized application of a stylus, the dye intermediate material orchromogenic compound is released and transferred to an underlying copysheet having an acidified, adsorbent coating comprising a material thatwill react with the dye intermediate causing a visible, colored mark atpoints where the microcapsules have been ruptured and the dyetransferred.

Transfer copy systems generally involve multipartforms including a CBsheet wherein the back of the sheet is coated with microcapsulescontaining the chromogenic compounds, a CFB sheet, which is a middlesheet having a coating on the front comprising an electron-acceptingmaterial of the Lewis acid type, such as an acid-treated clay, and acoating of the imageforming microcapsules on its underside or back side.The CB and CFB sheets are placed in register with a CF sheet which has acoating of the adsorbent clay on the front side thereof. Thus, whenlocalized pressure is applied to the front of the CB sheet, themicrocapsules coated on the back side thereof are ruptured to releasethe chromogenic material which reacts with the front of the CFB sheet toproduce an image, while the very same localized pressure is transferredthrough the CFB sheet to the underside thereof in order to rupturemicrocapsules thereunder and thus release the chromogenic material forreaction with the front of the CF sheet to produce an image thereon.

The relatively fragile nature of the microcapsules has presented variousproblems involving the coating of aqueous suspensions or dispersionscontaining such microcapsules onto paper webs or substrates.

In the past, elaborate precautions have been taken in order to avoidrupture of the microcapsules during the coating of the paper substratesin the formation of the CF and CFB sheets. Thus, air-knife coating headshave been employed almost exclusively when applying the aqueousmicrocapsular suspensions to the surface of a paper web in order toavoid the destruction of the structural integrity of the microcapsulesand thereby prematurely release the chromogenic compounds for reactionwith the clay.

Multi-part forms involving'transfer copy systems as described above havebeen conventionally employed in various applications, such as forinvoices for billing purposes, wherein it is desired to exclude data oncertain copies while including it on others. Thus, for example, acustomers copy of an order acknowledgement should not contain data whichmust be entered on copies to be used for internal purposes. Heretofore,the practice has been for the manufacturer of the carbonless copy paperto coat the entire surface of the CF and CB paper webs, for example,with the microcapsular suspension and the adsorbent clay suspension andship sheets of such paper to the printer. The printer must then employdesensitizing inks in order to block out certain selected areas of theform on one or more copies. The desensitizing ink prevents the colorlessdye, that is released from the CB coating, for example, from contactingthe CF surface and thereby forming an image. Unfortunately, such aprocedure is both uneconomic and wasteful, since it requires the generalapplication of the microcapsules and its co-re'active clay coating tothe entire surface of the paper web by the manufacturer, followed by adesensitization of large areas of the microcapsular coating by theprinter. Additionally, such a procedure has commonly caused distortionof the areas that are rendered inactive.

It has now been found that aqueous, microcapsular dispersions may beapplied in a localized manner by a coating system which involves passinga web, such as a paper web, continuously between a first roll and asecond roll, said first and second rolls being partially in nip-definingrelation, said first roll being an impression roll and said second rollbeing a printing roll, said printing roll being a roll having only aportion of its surface coated with a resilient material to provide araised, resilient printing head on the second roll. A coating of themicrocapsules, which contain a color-forming material, is formed on thepaper web as it passes between the first and second rolls at the nipformed between the first roll and the raised surface portion of thesecond roll. The coating therefore corresponds to the configuration ofthe raised indicia on the second roll. The coated paper is thereafterpassed to a drying zone wherein the microcapsular coating is dried.

Surprisingly, by employing a modified flexographictype roll, having araised portion in the form of the desired microcapsular coating, whichraised portion is formed of soft rubber or a similar synthetic,resilient material, the microcapsules may be locally applied to thepaper and in any desired configuration. Thus, whereas in the past theprinter had to employ a desensitizing material in order to desensitizeand therefore block out large areas of the CB sheets that were coatedover their entire surface with microcapsules, the printer, by employingthe present invention, can apply the microcapsular dispersion in anydesired configuration by merely changing the surface configuration ofthe raised, resilient portion of the second roll, i.e., the printingroll. Thus, the present invention eliminates the wasteful, generalizedcoating and desensitization of the CB sheets, and avoids the distortioncaused by the use of desensitizing inks.

Although it is not intended to limit the present invention by anyparticular theory or mechanism, it appears that the use of a soft,resilient, polymeric, raised coating applicator on the second roll, asthecoating head, in combination with a microcapsular dispersion whichhas a relatively high viscosity as compared with the usual microcapsularcoating dispersion, surprisingly permits the use of an offset printingtechnique for the localized or spot-printing of the microcapsulardispersion without rupturing the microcapsules and prematurely releasingthe chromogenic material contained therein.

Moreover, the adsorbent clay coating can likewise be applied to thefront side of a CF sheet in a configuration similar to that used forcoating of the CB sheet by the process of this invention, and theresulting CF sheet can be used in combination with a CFB or CB sheet,thereby additionally reducing the wasteful coating of the acid-claymaterial in a generalized manner.

In the accompanying drawing, wherein an illustrative embodiment of thepresent invention is disclosed,

FIG. 1 is a schematic elevational view of a coating system embodying thefeatures of the present invention;

FIG. 2 is a perspective showing a section of the printing roll of thepresent invention;

FIG. 3 is an enlarged section of a CB sheet produced in accordance withthe practice of the present invention; and

FIG. 4 is an enlarged section of a two sheet unit manifold.

Referring now to FIG. 1, coating pan is provided with an aqueous,microcapsular dispersion 12. The chromogenic compound-containingmicrocapsules present in the dispersion may be provided by any suitableprocess, whether physical or chemical, so long as the microcapsulesprocess sufficient structural integrity to withstand the coatingpressures to which they are subjected by the apparatus hereinafterdescribed.

The microcapsules to be coated onto the copy paper may have diametersranging from 0.1 to several hundred microns. However, capsules having anaverage diameter in the range from 3 to 5 microns are preferred fortransfer copy systems.

Preferably, the microcapsular dispersion 12 shown in FIG. 1 contains asuitable binder, such as carboxymethyl cellulose, methyl cellulose,starch, casein, polyvinyl alcohol, polyvinyl acetate latex, andstyrenebutadiene latex. Alternatively, binders such as urea formaldehydeor melamine formaldehyde condensates may be employed.

An aqueous dispersion of the microcapsules may be used directly asformed in the coating dispersion 12. However, it is preferred to subjectthe microcapsular dispersion to a spray drying operation in order toadditionally cure the capsule walls. The dry microcapsules obtained fromthe spray drying unit are redispersed into an aqueous medium including asuitable binder, such as carboxymethyl cellulose.

The lower portion of the pickup roll 14 dips into the aqueous suspensionof the microcapsules to receive a layer of a microcapsular coating. Aportion of this coating is transferred to form a layer on the peripheralsurface of transfer roll 16. Pickup roll 14 may be suitably a steelsurfaced roll, while transfer roll 16 is provided with a resilientblanket, fabricated from rubber or a synthetic resilient material. Forexample, the resilient blanket may have a three-ply fabric base on onesurface of which is a skim coat of a suitable rubber compound 0.12 to0.015 inch thick. The rubber blanket may be wrapped around the transferroll and held under a tension of about 50 pounds per inch of width, forexample.

The thickness of the ultimate coating of the microcapsules may becontrolled by adjusting the gap between rolls 14 and 16. Thus, openingor closing the gap between rolls l4 and 16 can regulate the amount ofmicrocapsular coating that is metered onto the transfer roll 16. The useof a rubber blanket 18 reduces the impact upon the microcapsules upontransfer of the microcapsular dispersion coating material from theblanket 18 to the printing cylinder 20. Printing cylinder 20 may be ametal roll having the desired raised, flexible, resilient printing head22 adhered to the surface thereof. Printing head 22 may be made ofresilient material which is similar to blanket l8 and thus would includea rubber plate, for example, formed of a resilient, synthetic material.

Referring now to FIG. 2, printing head 22 is shown as a rectangularrubber plate. Thus, for example, plate 22 may have a height of one-halfinch or the like and have a width and length of 2-4 inches, for example.After picking up a microcapsular coating on its surface from blanket 18,plate 22 is transferred to paper web W by adjusting the desired nippressure between the top surface of plate 22 and impression roll 24.Suitable nip pressures include between about 2 and about 200 preferablybetween and about pounds per square inch.

The configuration of printing head 22 may be varied to meet the needs ofthe particular business form. Thus, a very narrow strip of themicrocapsular coating may be applied over a very small portion of thepaper web, and the configuration of the strip may be varied fromrectangular to any geometrical shape and dimension as desired. Thecoating surface 23 of the printing head 22 preferably has the samecontour as the surface of the roll to which it is attached. Furthermore,more than one printing head may be employed, if desired, in order toprovide a series of closely spaced microcapsular coatings. Regardless ofthe configuration that is utilized for printing head 22, the process ofthe present invention permits the localized or spot printing of amicrocapsular dispersion onto a paper web and avoids the wasteful andexpensive application of a microcapsulardispersion over the entire widthof a paper web or sheet. Thus, for example, rubber plate 22 may have a 2inch by 4 inch surface with a one-half inch depth, and be placed in thecenter of the surface of the printing cylinder 20. This technique may beapplied to the CB sheet or the CB portion of a CFB sheet. Similarly, aspreviously mentioned, this technique can be used concurrently to apply aclay dispersion to local areas of a CF sheet or the front portion of aCFB sheet.

The process of the present invention can be used to apply localizedcoatings of microcapsules to all multipart business forms, credit cardforms, etc., i.e., in any application where it is desired to restrictthe amount of information provided from one sheet to another.

Suitably, the pressures to which the microcapsules are subjected in thenip formed between plate 22 and roll 24 are in the range of betweenabout 5 and about 50 psi, preferably between about 5 and about 10 psi.Accordingly, the microcapsules utilized in the present invention musthave sufficient structural integrity to withstand pressures up to thenip pressure.

After the microcapsular dispersion has been applied to the underside ofweb W in the desired configuration, the web is passed to a drying zone26 where the paper web having the coating thereon is subjected to anysuitable temperature conditions in order to dry the microcapsularcoating. Preferably, the drying zone 26 is a drying oven and is providedwith infrared heaters 28 and hollow metal tubes 30. The metal tubescontain perforations, such as round holes, which permit the introductionof air into the drying zone which can impinge on the back or uncoatedside of web W. Suitable air velocities include between about 2000 andabout 10,000 cubic feet per minute, preferably 6000 cubic feet perminute at temperatures between about 100 and about 300 F, preferably190F. Of course, the drying conditions will vary depending upon theparticular press'speeds, i.e., the speed at which web W is passedthrough the drying oven. However, such conditions are suitable for pressspeeds in the range of 100 to 800 feet per minute.

After the web W exits the drying oven, it is passed to a wind-up roll 32which is powered to wind the coated web onto the roll. Various guiderollers and tensioning rollers may be suitably employed as needed.However, their use is conventional and has not been illustrated in thedrawing.

FIG. 3 illustrates a sectional view of a copy sheet 36 having a surface40 with a microcapsular coating 38 printed thereon, wherein theremaining portions of the surface 40 is devoid of microcapsules.Suitable coat weights for the microcapsular coating include betweenabout 1 and about 4 pounds per ream of paper (3300 square feet),preferably about 3 pounds per ream.

As previously mentioned, any suitable process can be used for formingthe microcapsules for use in the present process. However, a preferredmethod for forming the microcapsules used in the coating process of thepresent invention involves providing an aqueous solution of awater-soluble, polymeric, film-forming, emulsifying agent, such aspolyvinyl alcohol, which emulsifier possesses hydroxyl groups, andthereafter forming an emulsion by admixing a water-immiscible, oilymaterial containing an oil-soluble, non-polymeric, crosslinking agentfor the emulsifying agent selected from the group consisting ofpolyfunctional isocyanates and orthoesters of Group IV elements. Thecross-linking agent interacts with the hydroxyl groups of the polymericemulsifying agent to form a solid, cross-linked, resinous capsule wall.In addition to the cross-linking agent, the oily material containssuitable chromogenic material, such as a combination of crystal violetlactone and benzoyl leucomethylene blue.

Thus, in general, the process for providing the chromogenic-containing,pressure-rupturable microcapsules involves admixing:

A. a water-immiscible, oily material containing an oil-soluble,non-polymeric cross-linking agent selected from the group consisting ofa polyfunctional isocyanate and an ortho ester of a Group IV element,and a chromogenic material; and

B. an aqueous solution of a hydroxyl groupcontaining, polymericemulsifying agent; said admixing being conducted under conditions toform an oil-inwater emulsion wherein said oily material is dispersed inthe form of microscopic emulsion droplets in an aqueous, continuousphase, reacting said cross-linking agent with said polymeric emulsifyingagent and thereby surrounding each of the droplets with a solid,cross-linked capsule wall. Preferably, the polymeric emulsifying agentis the sole reactant for the crosslinking agent.

During the formation of the microcapsules, the reaction of thecross-linking agent with the polymeric emulsifying agent, i.e., thecuring step, may be conducted at any suitable temperature, for example,between ambient temperature and about 100C, for periods of time between1 and 24 hours. The upper temperature at which the curing step may beconducted is only limited by the temperature at which the emulsion willbreak, i.e., the stability limit of the emulsion. Preferably, thecross-linking reaction is conducted at a temperature at a range ofbetween 40 and C, for a period of 1 to 3 hours. Suitable ratios ofemulsifier to cross-linking agent in the formation of such microcapsulesinclude at least one part by weight of emulsifying agent per part ofcross-linking agent up to about parts by weight of emulsifier per partof cross-linking agent, preferably between about 4 and about 20 parts byweight of emulsifier per part of cross-linking agent.

Suitable oil soluble polyfunctional isocyanates that may be employed forproduction of the microcapsules include, for example,4,4-diphenylmethane diisocyanate, toluene diisocyanate, hexamethylenediisocyanate, triphenylmethane triisocyanate, mixtures of suchisocyanates, and adducts of such isocyanates with polyhydric alcohols,such as trimethylolpropane.

The ortho esters of Group IV elements which may be employed ascross-linking agents include the aliphatic and aromatic ortho esters ofGroup IV(a) and IV(b) elements, preferably the lower alkyl and arylortho esters of Group IV elements, such as tetraethyl orthosilicate,tetrapropyl orthosilicate, tetraphenyl orthosilicate, tetraethyltitanate, tetrapropyl titanate, tetrabutyl titanate, tetraphenyltitanate, tetraethyl germanate, tetrapropyl orthocarbonate, and thelike.

Suitable polyhydroxyl polymers useful as emulsifying agents includepolyvinyl alcohol, methyl cellulose, starch and the like.

Polyvinyl alcohol is especially preferred, and such material may beemployed in any of the available water-soluble grades, either fully orpartially hydrolyzed, high or low molecular weight. The especiallypreferred polyvinyl alcohols suitable for use in the present inventionare those grades known as the 88 percent (nominal) hydrolyzed, highmolecular weight products (e.g., commercially available as Covol 97-40from CPI, or Elvanol 50-42 from du Pont).

Substituted starches are the preferred form of starch for use as anemulsifier, and such material may be provided by any suitable process.For example, they may be provided by etherification of the starch ingranular form under non-gelatinizing conditions with a monofunctionaletherifying agent which provides the starch with etherlinked hydrophobicgroups. Thus, the starch granule will become more oleophilic due to thepresence of a high percentage of hydrophobic groups. The hydrophobicgroups may be, for example, alkyl groups having at least three carbonatoms, ayralkyl groups containing at least 7 carbon atoms, and the like.The term substituted starch as employed herein refers to a starch thathas been rendered more eleophilic due to an increase in hydrophobicgroups. A preferred substituted starch is an ether-linked benzol starch.The starches are described in US. Pat. No. 3,707,514 to Vassiliades etal, which is hereby incorporated by reference.

The polyfunctional isocyanate or ortho ester crosslinking agent isutilized in amounts sufficient to result in the formation ofmicrocapsules. The relative amounts will vary with the particular systemand may be easily determined in each case. The polymeric emulsifyingagent may be provided in relatively substantial amounts of, for example,at least 1 part by weight of emulsifier per part of cross-linking agent,with between about 4 and about 20 parts emulsifier per part by weight ofthe oil-soluble cross-linking agent being preferred. An especiallypreferred range of cross-linking agent based upon the oil is betweenabout I and 40 weight percent of cross-linking agent, preferably betweenabout 2 and 10 weight percent.

The emulsification may be conducted at any suitable temperature. Forexample, temperatures in the range of between and 100C are preferred,although temperatures outside of this range may also be utilized.Subsequent to emulsification, the microcapsular dispersion may be heatedto a temperature, for example, in the range of between about 40 and 80for a period of between 1 and 4 hours under conditions of mild agitationin order to accelerate the cross-linking reaction. The cross-linkingreaction may be otherwise conducted at ambient temperatures for longerperiods of time, e.g., 24 hours, while obtaining similar results.

The water-immiscible oily materials include liophilic materials whichare preferably liquid, such as oils, which will not mix with water andwhich are inert with regard to the components of the particular system.

Oils are the preferred nucleus materials, and preferred oily materialsinclude the aliphatic and aromatic hydrocarbon oils, such as kerosene,mineral spirits, naptha, xylene, toluene and the like. Also for exampleterpenes, such as terpentine; esters, such as dimethylpthalate,dioctylphthalate, dimethylazelate, methyl-2- ethylhexanoate,2-ethylhexyl acetate and the like may be employed. The amount ofemulsifying agent relative to the oily nucleus material employed willvary over a wide range depending upon the particular system. However,suitable amounts include between 5 and 100 parts by weight ofemulsifying agent per 100 parts by weight of oil, preferably between 10and 50 parts of emulsifying agent per 100 parts by weight oil.

Suitable chromogenic materials are wholly conventional in this art.Examples of the colorless dye intermediates which may be employed in theformation of the microcapsules include the leuco dyes, such as crystalviolet lactone, and derivatives of bis(p-dialkyl amino aryl) methanesuch as disclosed in US. Pat. Nos. 2,981,733 and 2,981,738, which dyeintermediates are colorless in an alkaline or neutral medium and reactto form a visible color in an acidic medium. Thus, when the capsulecontaining such compound is ruptured and the compound is discharged ontoan adsorbent, acidic electron-acceptor material, such as a paper webcoated with an organic or inorganic acid material, a visible colorappears on the adsorbent material at the point of contact.

Inhibitors may optionally be dispersed in the oily material along withthe dye intermediates. Such materials are helpful in preventing lightand heat degradation of the intermediates during the encapsulationprocedure, especially when elevated temperatures are required.Inhibitors are also considered to aid in the stabilization of thecolored marking on the copy sheet against the effects of the atmosphere.A small amount (generally 1 to 10 percent by weight of the dye) of aninhibitor, such as N-phenol 2-naphthlamine, may be used. The leuco dyeintermediates which are mentioned above are, in general, oil soluble.Oils that are inert with respect to the dye and in which the dye hasappreciable solubility, e.g., above 0.5 g of dye per 100 g of oil, arepreferable.

As previously mentioned, the microcapsules are preferably spray driedand redispersed, rather than utilized directly as produced.

The spray drying of the microcapsules may be accomplished by injectingthe chromogenic materialcontaining microcapsules into a spray drierchamber of tower nozzle spray drier at a feed rate of, for example, 50to 52 milliliters per minute while employing an inlet temperature ofabout 150F. The outlet temperature is lower, e.g., about 106F. Thecapsular solution is injected into the spray drying chamber from atwo-fluid type atomizer at a pressure of psig. The dry capsular materialis then collected and redispersed in an aqueous coating medium.Alternatively, the capsular suspension as produced may be injected intoa conical spray drier at an atomizing pressure of, for example, psig.Inlet temperatures and outlet temperatures for the spray dryingoperation may be varied, but preferably inlet temperatures are fromabout 150 to 250F, while the outlet temperatures are from to F.Similarly, the feed rate may be varied depending upon the particularmaterial undergoing the spray drying operation, and may be varied from20 to 75 milliliters per minute.

Regardless of whether the microcapsular coating dispersion 12 is formedfrom microcapsules as made directly, or subsequent to being spray driedand redispersed, the viscosity is thereafter adjusted to the desireddegree. The solids content of the microcapsules in water is generallyhigher in the coating dispersons of the present invention than thatemployed in the conventional coating operations previously employed formicrocapsules. The solids content of the microcapsular dispersion issuggested to be between about 5 and about 30 percent, preferably betweenabout 18 and about 25 percent, e.g., 22 percent by weight solids, andthereafter a suitable binder, such as carboxymethyl cellulose is addedto increase the viscosity of the dispersion to the desired extent. Asuitable viscosity range for purposes of the present invention includesbetween about 10 and about 300 centipoises, preferably between about 50and about 100 centipoises.

The procedure illustrated in FIG. 1 can be employed for the applicationof a localized coating of an electronaccepting material in the mannerdescribed for local application of microcapsules. Although anyelectronaccepting material may be applied to the web W by means ofprinting head 22, the preferred electronaccepting material is an acidicsolid, such as bentonite, kaolin, montmorillonite, other acidic clays,talc, aluminum silicate, calcium citrate, metal chlorides, or the like.The electron-accepting acidic clays are especially preferred.Accordingly, a coating suspension 12 of acidic clay, for example, isprovided in vessel 10 and pickup roll 14 dips into an aqueous suspensionof the clay and transfers a portion of the clay to transfer roll 16 andprinting head 22 as previously described. The viscosity of the coatingsuspension is adjusted by the addition of water to obtain a consistencysimilar to that of ofiset printing ink.

The aqueous clay coating is applied to the web and dried in oven 26 asdescribed previously in connection with the application of microcapsularcoating suspensions. The same printing heads may be used for the clayand the resulting web W will have the configuration shown in FIG. 4 asdescribed in connection with the microcapsular coating. The sameprinting head may be used for applying the microcapsular dispersion informing a CB and/or CFB sheet and for applying an acidic clay coating inorder to form a CF and/or CFB sheet.

The resulting sheets can be then utilized together in register with aminimum waste of coating materials.

In FIG. 4, the clay coated web W is provided with the local or spot claycoating 144 on surface 146 of the sheet 142. Superimposed over sheet 142is sheet 136 having a microcapsule coating 138 on its surface 140. Thecoating 138 has the same configuration as does coating 144 and is placedin register therewith. In actual use, the coatings are placed inphysical contact, and the localized pressure of a writing instrument onthe upper or uncoated surface of sheet 136 directly above the coating138 ruptures the capsules in the coating 138 and releases chromogenicmaterial for reaction with the clay coating 144 upon which a coloredimage is produced. Although FIG. 4 illustrates a two sheet couplet, theinvention can be utilized with a multisheet system having CFB sheetssanwiched in between other CFB sheets, if desired, with the top sheetbeing a CB sheet and the bottom sheet being a CF sheet. Also, anymodifications may be utilized. For example, sheet 36 of FIG. 3 may beused with a CF sheet having its entire surface coated with anelectron-accepting material, rather than merely a local coating thereof.Conversely, sheet 142 of FIG. 4 may be used with a CB sheet having amicrocapsule coating over its entire back surface. Similarly, althoughFIG. 4 shows a single local coating of microcapsules and clay, thesheets may be provided with numerous such coatings as needed.

The following examples illustrate the present invention.

EXAMPLE 1 diameter is obtained. The emulsion is then heated while undermild agitation at a temperature of 60C for 2 hours. The microcapsulardispersion is then injected into a spray drier chamber at a feed rate ofabout 50 milliliters a minute at an inlet temperature of about 150F andan outlet temperature of about 100F. The

resulting microcapsules are collected as a dry powder and areredispersed in water to obtain a solids content of about 24 percent byweight. Carboxymethyl cellulose and a'load bearing agent, e.g., starchor the like, are added to the dispersion to form a viscosity of 50centipoises.

EXAMPLE 2 Employing the apparatus shown in FIG. 1, coating pan isprovided with the microcapsular dispersion obtained in Example 1. Thedispersion is picked up by roll 14 and transferred to roll 16 whichmeters the microcapsular coating to plate 22 so as to provide a coatweight of about 2 to 4 pounds per 3,300 square feet of surface area toweb W. The dispersion is coated onto paper web W which is moving at aspeed of 400 feet per minute. After the web W receives the coating, theweb is passed to drying oven 26 containing the infrared heaters andreceives heated air on the upper side thereof at a velocity of 600 cubicfeet per minute and at a temperature of F. The web W is collected onwinder 34.

The resulting localized coating of microcapsules is placed in registerwith a CB sheet and tested. When a ballpoint pen is applied to the frontside of the CB sheet, a sharp blue mark is provided on the CF sheetadjacent the microcapsular coating.

EXAMPLE 3 The apparatus of FIG. 1 is employed to apply spot coatings ofan aqueous coating of active bentonite clay to a paper web to form a CFsheet. The clay slurry is diluted with water until it has theconsistency of offset printing ink. The clay is applied by plate 22 at acoat weight of 2 to 4 pounds per 3,300 square feet of paper. Thecoatings are dried in drying oven 26 employing the conditions used inExample 2. A sample of a CF sheet as produced herein is placed inregister with a sample of the CB paper produced in Example 2. Upon theapplication of localized pressure by means of a ballpoint pen, aninstantaneous blue image results on the localized area.

This invention has been described in considerable detail with particularreference to preferred embodiments, but it will be understood thatvariations and modifications can be effected within the spirt and scopeof the invention as described in the appended claims.

I claim:

1. A process for the production of a pressure sensitive sheet having alocal coating of microcapsules thereon, which comprises passing a webcontinuously between a first roll and a second roll, said first andsecond rolls being partially in nip-defining relation, said first rollbeing an impression roll and said second roll being a printing roll,said printing roll being a roll having only a portion of its surfacecoated with a resilient material to provide a raised, resilient printinghead on said second roll, said nip being formed between said first rolland the coating surface of said raised, resilient printing head, saidcoating surface of said printing head being provided with a coating ofmicrocapsules prior to passage of said printing head through said nip,and thereby forming a coating of microcapsules on said web as it passesthrough said nip in a configuration corresponding to said printingsurface of said printing head, said microcapsules containing achromogenic material and being capable of withstanding pressures of upto 50 psi without rupturing, and passing said coated web to a dryingzone wherein said microcapsular coating is dried.

2. The process of claim 1 wherein said raised printing head is providedwith a microcapsular coating by means of a transfer roll, said transferroll having a resilient surface.

3. The process of claim 2 wherein said transfer roll receivesmicrocapsules from a pickup roll, which, in turn, picks up microcapsulesfrom an aqueous dispersion of microcapsules.

4. The process of claim 1 wherein said microcapsules have wallscomprising polyvinyl alcohol cross-linked by a polyisocyanate.

5. The process of claim 1 wherein said printing head comprises a rubberplate having a rectangular shape.

6. The process of claim 5 wherein said printing head has a surface whichis between about 1 and about 8 inches in width, between about 1 andabout 12 inches in length.

7. The process of claim 1 wherein said drying zone is provided withinfrared drying means.

8. The process of claim 7 wherein the web is paper and is additionallysubjected to heated air which directly contacts the uncoated side ofsaid paper web.

9. The process of claim 1 wherein said chromogenic material is acombination of crystal violet lactone and benzoyl leuco methylene blue.

10. A process for the production of a copy sheet having a local coatingof an electron-accepting material of the Lewis acid type thereon, whichcomprises passing a web continuously between a first roll and a secondroll, said first and second rolls being partially in nipdefiningrelation, said first roll being an impression roll and said second rollbeing a printing roll being a roll having only a portion of its surfacecoated with a resilient material to provide a raised, resilient printinghead on said second roll, said nip being formed between said first rolland the coating surface of said printing head being provided with anaqueous coating of clay prior to passage of said printing head throughsaid nip, and thereby forming a coating of said clay on said web as itpasses through said nip in a configuration corresponding to saidprinting surface of said printing head and passing said coating paperweb having a local coating of clay thereon to a drying zone wherein saidclay coating is dried.

11. The process of claim 10 wherein said raised printing head isprovided with an aqueous clay coating by means of a transfer roll, saidtransfer roll having a resilient surface.

12. A pressure sensitive copy system comprising a transfer sheet havinga surface thereof provided with a local coating consisting essentiallyof pressurerupturable microcapsules in a predetermined configuration ononly a portion of said surface, said microcapsules containing achromogenic material and being capable of withstanding pressures of upto 50 psi without rupturing.

13. The copy system of claim 12 wherein said transfer sheet issuperimposed over a receiving sheet, said receiving sheet having asurface thereof provided with a local coating consisting essentially ofan electronaccepting clay in a predetermined configuration on only aportion of a surface of said receiving sheet, said microcapsule coatingand said clay coating being positioned in physical contact with eachother.

14. The copy system of claim 13 wherein the configuration of saidmicrocapsule coating and that of said clay coating is substantiallyidentical, and said coatings are positioned in substantial register withone another.

15. The copy system of claim 12 wherein said microcapsule coating coversonly a minor portion of said surface.

16. The copy system of claim 12 wherein said microcapsules have wallscomprising polyvinyl alcohol crosslinked by a polyisocyanate.

1. A PROCESS FOR THE PRODUCTION OF A PRESSURE SENSITIVE SHEET HAVINGALOCAL COATING OF MICROCAOULES THEREON, WHICH COMPRISES PASSING A WEBCONTINUOUSLY BETWEEN A FIRST ROLL AND A SECOND ROLL, SAID FIRST ANDSECOND ROLLS BEING PARTIALLY IN NIPDEFINING RELATION, SAID FIRST ROLLBEING AN IMPRESSION ROLL AND SAID SECOND ROLL BEING A PRINTING ROLL,SAID PRINTING ROLL BEING A ROLL HAVING ONLY A PORTION OF ITS SURFACECOATED WITH A RESILIENT MATERIAL TO PROVIDE A RAISED, RESILIENT PRINTINGHEAD ON SAID SECOND ROLL, SAID NIP BEING FORMED BETWEEN SAID FIRST ROLLAND THE COATNG SURFACE OF SAID RAISED, RESILIENT PRINTING HEAD, SAIDCOATING SURFACE OF SAID PRINTING HEAD BEING PROVIDED WITH A COATING OFMICROCAPULES PRIOR TO PASSAGE OF SAID PRINTING HEAD THROUGH SAID NIP,AND THEREBY FORMING A COATING OF MICROCAPTION CORRESPONDING TO SAIDPRINTING SURFACE OF SAID PRINTING TION CORRESPONDING TO SAID PRINTINGSURFACE OF SAID PRINTING HEAD, SAID MICROCAPSULES CONTAINING ACHROMOGETIC MATERIAL AND BEING CAPABLE OF WITHSTANDING PRESURES OF UP TO50 PSI WITHOUT RUPTURING, AND PASSING SAID COATED WEB TO A SYING ZONEWHEREIN SAIC MICROCAPSULAR COATING IS DRIED.
 2. The process of claim 1wherein said raised printing head is provided with a microcapsularcoating by means of a transfer roll, said transfer roll having aresilient surface.
 3. The process of claim 2 wherein said transfer rollreceives microcapsules from a pickup roll, which, in turn, picks upmicrocapsules from an aqueous dispersion of microcapsules.
 4. Theprocess of claim 1 wherein said microcapsules have walls comprisingpolyvinyl alcohol cross-linked by a polyisocyanate.
 5. The process ofclaim 1 wherein said printing head comprises a rubber plate having arectangular shape.
 6. The process of claim 5 wherein said printing headhas a surface which is between about 1 and about 8 inches in width,between about 1 and about 12 inches in length.
 7. The process of claim 1wherein said drying zone is provided with infrared drying means.
 8. Theprocess of claim 7 wherein the web is paper and is additionallysubjected to heated air which directly contacts the uncoated side ofsaid paper web.
 9. The process of claim 1 wherein said chromogenicmaterial is a combination of crystal violet lactone and benzoyl leucomethylene blue.
 10. A process for the production of a copy sheet havinga local coating of an electron-accepting material of the Lewis acid typethereon, which comprises passing a web continuously between a first rolland a second roll, said first and second rolls being partially innip-defining relation, said first roll being an impression roll and saidsecond roll being a printing roll being a roll having only a portion ofits surface coated with a resilient material to provide a raised,resilient printing head on said second roll, said nip being formedbetween said first roll and the coating surface of said printing headbeing provided with an aqueous coating of clay prior to passage of saidprinting head through said nip, and thereby forming a coating of saidclay on said web as it passes through said nip in a configurationcorresponding to said printing surface of said printing head and passingsaid coating paper web having a local coating of clay thereon to adrying zone wherein said clay coating is dried.
 11. The process of claim10 wherein said raised printing head is provided with an aqueous claycoating by means of a transfer roll, said transfer roll having aresilient surface.
 12. A PRESSURE SENSATIVE COPY SYSTEM COMPRISING ATRANSFER SHEET HAVING A SURFACE THEREOF PROVIDED WITH A LOCAL COATINGCONSISTING ESSENTIALLY OF PRESSURE-RUPTABLE MICROCAPSULES IN APREDETERMINED CONFIGURATION ONLY ONLY A PORTION OF SAID SURFACE, SAIDMICROCAPSULES CONTAINING A CHROMOGENIC MATERIAL AND BEING CAPABLE OFWITHSTANDING PRESSURES OF UP TO 50 PSI WITHOUT RETURNING.
 13. The copysystem of claim 12 wherein said transfer sheet is superimposed over areceiving sheet, said receiving sheet having a surface thereof providedwith a local coating consisting essentially of an electron-acceptingclay in a predetermined configuration on only a portion of a surface ofsaid receiving sheet, said microcapsule coating and said clay coatingbeing positioned in physical contact with each other.
 14. The copysystem of claim 13 wherein the configuration of said microcapsulecoating and that of said clay coating is substantially identical, andsaid coatings are positioned in substantial register with one another.15. The copy system of claim 12 wherein said microcapsule coating coversonly a minor portion of said surface.
 16. The copy syStem of claim 12wherein said microcapsules have walls comprising polyvinyl alcoholcross-linked by a polyisocyanate.